Reverse latitudinal diversity gradients, exceptions that prove the rule?

Abstract

Morales-Castilla, I., García-Valdés, R. 2014. Reverse latitudinal diversity gradients, exceptions that prove the rule? Ecosistemas 23(1):4-12. Doi.: 10.7818/ECOS.2014.23-1.02

Most taxonomic groups follow a Latitudinal Diversity Gradient and tend to be more diverse as we approach the tropics. Nevertheless, there are important exceptions to such pattern, which can provide with additional information on the mechanisms that generate it. Despite the large amount of hypotheses proposed to explain diversity gradients, it is still necessary to find hypotheses able to explain both the general pattern and the exceptions to it. Niche conservatism and the time-for-speciation effect meet this requirement by predicting higher diversity of organisms in the environments where they have had longer periods to diversify, based on an evolutionary retention of the conditions under which different taxonomic groups originated. Here we review the scientific literature tackling the study of exceptions to the Latitudinal Diversity Gradient, discuss the explanations for reverse patterns in connection to niche conservatism and offer examples of how biogeographic history can be used as an auxiliary source to infer ancestral niches. While it is likely that multiple mechanisms generate current diversity patterns, explanations such as niche conservatism and time-for-speciation bring us closer to the understanding of how large scale diversity patterns have been configured along the evolutionary history of the organisms.